1. Field of the Invention
The present invention relates, in general, to a refrigerator with a door locking mechanism. More particularly, the invention relates to a refrigerator controller for operating the door locking mechanism of the refrigerator in accordance with a command signal from a host-computer connected therewith.
2. Description of the Prior Art
Guest rooms of lodging facilities such as hotels have recently been furnished with refrigerators which store beverages such as canned or bottled liquor and food so that guests can enjoy them as they desire. Many lodging facilities have adopted central control systems to centrally administer refrigerators in guest rooms. Refrigerators in guest rooms are connected with a host-computer at a front desk, for example, through a bidirectional transmission line and are controlled thereby. Data concerning the number and kind of goods taken from each refrigerator is sent to the host-computer through the bidirectional transmission line. The guest, when he checks out, pays his food and drink charges which the host-computer calculates from the data at the front desk.
Differing from a refrigerator for home use, the refrigerators in guest rooms are usually provided with door locking mechanisms for preventing beverages and food, refrigerated in a guest room where no one checks in, from being taken out fraudulently. The door locking mechanism of each refrigerator is also controlled by the host-computer with each refrigerator receiving a lock or an unlock command signal through the bidirectional transmission line from the host-computer. The guest can open a door of each refrigerator only when the host-computer sends the unlock command signal thereto through the bidirectional transmission line. The period of time during which the host-computer generates the lock or the unlock command signal is previously determined by an administrator of the lodging facility.
An example of such a central control system for refrigerators with a door locking mechanism is disclosed in Japanese Utility Model Publication No. 59-12671, filed Nov. 29, 1979 in the name of Satoru Hibino. In Japanese Utility Model Publication No. 59-12671, each refrigerator in a guest room is connected with a central administering device including a microprocessor through a bidirectional transmission line. Each refrigerator is also provided with a door locking mechanism comprising an electromagnetic solenoid. When an unlock command signal is received from the central administrating device through the bidirectional transmission line, the electromagnetic solenoid is energized and a door of the refrigerator is kept unlocked. Accepting a lock command signal causes the electromagnetic solenoid to deenergize and the door is kept locked. Energizing the electromagnetic solenoid of the door locking mechanism is performed with a DC power transformer supplying DC power thereto. From the standpoint of decreasing production cost, it is desirable for the capacity of DC power transformer to be designed so that the DC power transformer can supply such an amount of DC power to the electromagnetic solenoid that the electromagnetic solenoid generates a holding force which is enough to keep the door in an unlocked or locked condition. The holding energy for the electromagnetic solenoid is generated by a steady state current flowing therethrough.
As is well known, however, the instantaneous current initially flowing through an electromagnetic solenoid is larger than the steady-state current flowing therethrough after initial energization. Therefore, the power supply voltage which is supplied to the electromagnetic solenoid from the DC power transformer may drop to an unacceptably low value as a result of the initial current drawn by the solenoid and the driving force necessary for the electromagnetic solenoid to change the state of the door cannot be obtained.
In order to solve this problem, in the prior art central control system for refrigerators with a door locking mechanism, the DC power transformer in each refrigerator had to be designed to have a larger capacity than necessary for steady-state operation.